With the recent development of information communication technology, a variety of wireless communication techniques are being developed. From among the techniques, a WLAN is technique which enables wireless access to the Internet at homes or companies or in specific service providing areas using mobile terminals, such as a Personal Digital Assistant (PDA), a laptop computer, and a Portable Multimedia Player (PMP), based on radio frequency technology.
Lots of standardization tasks are being carried out since Institute of Electrical and Electronics Engineers (IEEE) 802 (that is, the standard organization for WLAN technique) was set up on February, 1980.
The initial WLAN technique was able to support the bit rate of 1 to 2 Mbps through frequency hopping, band spreading, and infrared communication by using a 2.4 GHz frequency band in accordance with the IEEE 802.11 standard, but the recent WLAN technique can support a maximum bit rate of 54 Mbps using Orthogonal Frequency Division Multiplex (OFDM) method. Furthermore, in the IEEE 802.11 standard, the standards of various techniques, such as the improvements of Quality of Service (QoS), the compatibility of Access Point (AP) protocols, security enhancement, radio resource measurement, wireless access vehicular environment for vehicle environments, fast roaming, a mesh network, interworking with an external network, and wireless network management, are put to practical use or being developed.
With the spread of WLAN being activated and applications using WLAN being diversified, there is a need for a new WLAN system for supporting the throughput higher than the data processing speed supported by the IEEE 802.11n standard. A Very High Throughput (VHT) WLAN system is one of IEEE 802.11 WLAN systems recently proposed in order to support the data processing speed of 1 Gpbs or higher. The term ‘VHT WLAN system’ is arbitrary, and a feasibility test for 8×8 MIMO and a system using a channel bandwidth of 80 MHz or higher is in progress in order to provide the throughput of 1 Gpbs or higher.
To secure a channel having a wide frequency bandwidth in the frequency band used by the WLAN system may be practically difficult. For example, in an ISM (Industrial Scientific and Medical) band used by the WLAN system, various devices, heterogeneous communication systems, and legacy systems, such as IEEE 802.11a/b/g/n, which use the ISM (Industrial Scientific and Medical) band, coexist. In order to obtain a channel having a wide frequency bandwidth in this environment, a scheme for aggregating and utilizing a plurality of non-contiguous channels is being researched.
When it is used a multi-channel obtained by aggregating a plurality of non-contiguous channels by the WLAN system, a link adaptation method for each of sub-channels forming the multi-channel, a problem, such as a reduction in transmission efficiency that may occur when transmitting data on a plurality of spatial streams through the multi-channel, and a protocol for solving the transmission synchronization problem of data packets need to be taken into consideration.